Session: 09-03-02: Current and Tidal Energy: Hydrodynamic Analysis

Paper Number: 105021

105021 - Computational Fluid Dynamics Study of a Cross-Flow Marine Hydro-Kinetic Turbine and the Combined Influence of Struts and Helical Blades 

A computational fluid dynamics (CFD) study was performed for a cross-flow marine hydro-kinetic (MHK) turbine. The high-fidelity code, STAR-CCM+, was used for the three-dimensional unsteady Reynolds averaged Navier-Stokes (RANS) analysis. A convergence and uncertainty study was performed for both the spatial and temporal discretization. Cross-flow turbines experience continually varying angles of attack, even in a uniform steady inflow. This leads to a periodic load pattern and can result in dynamic stall for many tip-speed ratios. Prediction of this phenomenon requires a tightly refined mesh near the rotor, especially in the boundary layer and near the trailing edge. The impact of various mesh densities and structures in this region, as well as turbulence models and time steps, was studied. Modeling suggestions for cross-flow turbines based on these results are discussed in this work. The base turbine configuration in the study is the RivGen, designed by the Ocean Renewable Power Company (ORPC). The turbine features support struts and helical foils. Helical blades smooth out the load profile throughout a rotation, but also induce some spanwise flow. This effect has been found to be an important factor for some turbines’ power performance. Struts are practically necessary, but they can lead to significant losses in power production both due to their own resistance to rotation and to their effect on the flow over the blades. This study assesses the combined impact of struts and helical foils on both power performance and blade loading. The relative impact of struts is compared for both helical and straight bladed rotors. Distributed loads are analyzed in the spanwise direction for each foil, and the time and pattern of stall is studied. The wake development and wake crossing on the downstream stroke of the rotation are also given significant consideration.     

Presenting Author: Will Wiley National Renewable Energy Laboratory

Presenting Author Biography: Will Wiley received a M.Sc. in Offshore Engineering from the Delft University of Technology and a M.Sc. of Wind Energy from the Norwegian University of Science and Technology in 2021. Before that he received a B.Sc. of Naval Architecture and Marine Engineering from Webb Institute in 2019. He is now a researcher at the National Renewable Energy Laboratory working on both high-fidelity and mid-fidelity hydrodynamic modeling for marine energy devices and floating offshore wind turbines.

Authors:

Will Wiley National Renewable Energy Laboratory
Thanh Toan Tran National Renewable Energy Laboratory
Michael Lawson National Renewable Energy Laboratory
Matthew Barrington Ocean Renewable Power Company